<!DOCTYPE html>
<html>
<body>
<script>
function doe(aEl) {
var doc = aEl.contentDocument;
doc.designMode = 'on';

try {
doc.execCommand("insertHTML",false,'some text');
} catch(e) {
  document.getElementById('result').innerHTML = e;
}
}
</script>

<iframe onload="doe(this)"></iframe><br>
<pre id="result" style="background-color: red; width: 300px; white-space: -moz-pre-wrap;"></pre>
</body>
</html>
